Level means

ABSTRACT

A system for raising and lowering a platen, which is hinged along one edge, by a plurality of rams which have their piston rods pivoted adjacent to the opposite edge of the platen while maintaining the platen in a substantially level condition even if the platen is unequally loaded. The system includes a master ram and a plurality of slave rams. The master ram is operated in response to a command signal which is modulated by an error correcting feedback signal. The feedback signal is generated by an angular position-sensing potentiometer. The slave rams are operated in response to a signal generated in response to transient fluid pressures developed in the master ram so that the slave rams all attain the same pressure as that present in the master ram. A level-comparing device is provided which compares the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand. A signal is generated in response to any difference in the level of the slave rams and this signal is employed to correct and modulate the signal generated in response to pressure in the master ram.

United States Patent Ponter 1451 Feb. 1, 1972 [54] LEVEL MEANS [57]ABSTRACT [72] Inventor: Robe t J, P te (il h P A system for raising andlowering a platen. which is hinged along one edge, by a plurality oframs which have their piston [73] Asslgnee: Engmeenng Company rodspivoted adjacent to the opposite edge of the platen while [22] Fil d;on, 1, 1970 maintaining the platen in a substantially level conditioneven if the platen is unequally loaded. The system includes a masterApp! 77057 ram and a plurality of slave rams. The master ram is operatedin response to a command signal which is modulated by an [52] U.S. Cl...9l/41l R, 91/412, 60/97 E, rr r rr ting feedback signal. The feedbacksignal is 60/97 L generated by an angular position-sensingpotentiometer. The [51] Int. Cl ..Fl5b 11/22 slave rams are operated inresponse to a signal generated in [58] Field of Search ..9l/411 R, 411B, 412; 60/97 E, response to transient fluid pressures developed in themaster 60/97 L ram so that the slave rams all attain the same pressureas that present in the master ram. A level-comparing device is pro-References Cited vided which compares the actual extended level of atleast one slave ram on the one hand with the actual extended level of atUNITED STATES PATENTS least one other slave ram on the other hand. Asignal is 2,487,402 11/1949 generated in response to any difference inthe level of the 2,984,072 5/1961 slave rams and this signal is employedto correct and modulate 3,381,588 5/1968 the signal generated inresponse to pressure in the master ram. 3,381,833 5/1968 3,433,1253/1969 Gemmell ..91/411 R x 5 Claims 3 Drawing Figures PrimaryExaminer-Edgar W. Geoghegan Attorney-McNenny, Farrington, Peame andGordon LEVEL MEANS This invention relates to platens having a raisingand lowering system which maintains the platen in a level conditionduring such operations. This invention is particularly suitable for usein assembly operations wherein a structural section of an article isassembled in a horizontal position on an assembly platen. The assemblyplaten is hinged along one edge. After the component is assembled on theplaten, a plurality of rams raise the opposite edge of the platen untilthe platen is in a substantially vertical position. During thisoperation the article is supported by a support platen which is pivotedto the hinge for the assembly platen. Rams on the opposite edge of thesupport platen permit the support platen to be lowered as the assemblyplaten is raised. In this manner, the assembled article is rotatedthrough 90 so that it may be assembled or joined to previously assembledcomponents. This operation is particularly useful in ship-buildingtechniques wherein hull sections are assembled in a-vertical positionand then raised to a horizontal position so that the assembled hullsection may be joined to the mail hull. It should be appreciated thatwhile the hull section is raised to a horizontal position, it isimperative that the platen remain in a level position since any bendingstresses in the hull section may cause weld breakage of cracking and mayresult in an imperfect fit between the hull section and the remainder ofthe hull.

This invention provides a system which. maintains a level platenposition during raising and lowering operations even under unequalloading conditions on the rams. According to this invention, a masterram is provided which is raised or lowered in response toa commandsignal. The command signal to the master ram is modulated and correctedby a feedback signal, which is generated by a position sensor, which maybe a potentiometer that generates a linear signal in response to theangular position of the platen. The pressure in the master ram issensedby a pressure transducer and the pressure transducer generates asignal to a plurality of slave rams. The slave rams are provided with alevel-sensing device that compares the level of one or a group of slaverams on the one hand with the level of another or a group of slave ramson the other hand. A signal is generated in response to any differencein level between the slave rams and that signal corrects and modulatesthe signal generated by the pressure transducer. Thus, any unequalloading on the rams which would tend to generate a false pressure signalis corrected by the signal generated in response to the true level ofthe slave rams.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing aplaten raising, lowering, and leveling system in accordance with thisinvention.

FIG. 2 is a diagrammatic illustration of the control system according tothis invention.

FIG. 3 is a cross-sectional view of a leveling means employed inconjunction with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, an assembly platen 10 and a support platen 11 are illustratedin FIG. 1. The platens l and 11 are identical in construction and forpurposes of simplicity and clarity, only the platen will be described indetail. Furthermore, the platens 10 and 11 have identical raising andlowering systems and the system employed in conjunction with the platen10 will be described in detail.

The platen 10 includes a plurality of support beams 12, 13, l4, 15, 16,17, I8, 19, 20, and 21. The beams 12 through 21 are hinged at theirlower ends to a shaft 22 for pivotal movement from a horizontal positionthrough an angle of 90 to a vertical posltlon. The beams 12 through 21are joined together by cross beams 23 and carry an assembly platen bed24.

For each beam 12 to 21. there is provided a ram 25, 26, 27, 28. 29, 30,31, 32, 33, and 34. respectively. Each ram 25 to 34 has a piston rod 35which is pivotally connected to a beam 12 to 21 by a pin 36. Each ram 29has a cylinder base 37 pivoted in a trunnion 38.

Each ram 25 to 34 has a pressure chamber 39 (FIG. 2) which is suppliedwith fluid from a pressure source 40. Although the pressure source isillustrated in FIG. 2 as separate units, it is to be understood that thesource 40 may comprise a single source, such as a pump. The pressurefluid is admitted to and exhausted from each pressure chamber 39 by aline 41, and flow through the line 41 is governed by a fourway, closedcenter valve 42. Each valve 42 is operated by a control means 43 whichoperates its valve 42 to exhaust fluid from or to supply fluid to thepressure chamber 39 in response to a particular signal to the controlmeans. Absence of a signal to the control means will maintain the valve42 in its illustrated closed position. Each control means 43 receives asignal from its own servocontroller 44.

In the illustrated embodiment, the ram 29 comprises a master ram. As waspreviously indicated, the master ram 29 is pivoted to the beam 16. Alsoassociated with the beam 16 is an angular motion sensor 45 whichproduces a linear voltage signal as a function of the actual angularposition of the beam 16. The angular motion sensor 45 may comprise anangular motion potentiometer having a mechanical input signal whichproduces a corresponding linear output signal voltage. The mechanicalinput signal to the angular motion sensor comprises a segment gear 46mounted on the beam 16 and a pinion gear 47 which engages the segmentgear 46. Rotation of the pinion gear 47 produces an output signal fromthe potentiometer as a linear function of the angular displacement ofthe pinion gear 47. The output signal generated by the angular motionsensor is transmitted by a lead 48 to the servocontroller 44 associatedwith the master ram 29.

The valve 42 associated with the master ram 29 is operated in responseto a signal generated by a command signal generator 49. The signalgenerated by the command signal generator is transmitted to theservocontroller and is compared to the signal generated by the angularmotion sensor. Thus, the command signal is modulated and corrected bythe signal generated by the angular motion sensor. If these signalsmatch and cancel each other, the servocontroller has a zero output tothe valve control means 43 and the valve 42 remains in its closedcondition. If, however, the command signal exceeds the signal generatedby the angular motion sensor, the valve 42 is shifted to admit fluid tothe pressure chamber 39. If, on the other hand, the angular motionsensor senses an angular position exceeding that position determined bythe command signal generator, a signal is transmitted to the valvecontrol means 43 which shifts the valve 42 to a position which exhaustsfluid from the pressure chamber 39. Thus, to raise the assembly platento a predetermined position, a command signal is generated, and thatsignal has a value which corresponds to a value which is sufficient tooperate the valve 42 so that the ram 29 attains a position correspondingto the predetermined position. Any error in this position is sensed bythe angular motion sensor 45 and a signal is transmitted to theservocontroller 44 to correct any such error.

Pressure transducers 51, 52, 53, 54, 55, 56, 57, 58, 59, and 60 arerespectively provided on the rams 25 to 34. These pressure transducersare associated with pressure cells which communicate with the pressurechambers 39 and include strain gauges which transmit a signal which isproportional to the amount of pressure in the pressure chambers 39.Signals produced by the pressure transducer 55 associated with themaster ram 29 are transmittedby a lead 61 to the servocontrollers 44other than the servocontroller 44 associated with the master ram 29.

Thus, as the master ram 29 is raised in the previously described manner,the pressure in the master ram 29 increases and the pressure transducer55 associated with the master ram 29 transmits a command signal to eachother servocontroller 44. In response to this command signal. each othercontroller 44 transmits a signal to each other valve operating means 43to operate each other valve 42 to match the pressure in the slave rams25-28 and 30-34 with that pressure obtained in the master ram 29. Thepressure transducers 51-54 and 56-60 associated with the slave ramsgenerate an error correcting signal which is fed back into theservocontroller 44 to modulate the signal received from the pressuretransducer 55 associated with the master ram 29.

In the illustrated embodiment, the ram 30 is a slave ram with respect tothe pressure in the master ram 29, The ram 30 may also serve as a backupram in the system so that the ram 30 may become the master and the ram29 may be slaved to the pressure in the ram 30. in this regard, itshould be noted that the ram 30 is provided with an angular motionsensor 50 so that the control systems associated with the ram 30duplicate those associated with the ram 29. To convert the ram 30 to amaster ram and the ram 29 to a slave ram, the command signal generator49 is connected to the servocontroller 44 associated with the ram 30 anddisconnected from the servocontroller 44 associated with the ram 29. Thesignal generated by the pressure transducer 56 is transmitted to theservocontrollers 44 associated with the rams 25- 29 and 31-34 and thesignal generated by the pressure transducer 55 is transmitted only tothe servocontroller 44 associated with the ram 29. These operations maybe conveniently performed by suitable switch means (not shown).

As the master ram 29 is raised, the slave rams 25 to 28 and 30 to 34 areraised and the pressure in the slave rams corresponds to the pressuregenerated in the master ram. However, due to unequal loading conditionswhich may exist on the assembly platen, the platen may not be level eventhough equal pressures exist in all of the rams. To compensate for levelerrors among the slave rams therefor, a leveling means is provided.

The leveling means according to this invention includes level sensors70, 71, 72, and 73 pivotally connected to the beams 15, 12, 18, and 21,respectively. Since the leveling sensors 70, 71, 72, and 73 areidentical, only the sensor 71 will be described in detail.

Referring now to FIG. 3, the leveling sensor 71 includes a reservoir 74which is in the form of a cup. The top of the reservoir 74 is closed bya neck 75 which is fixed to the open mouth of the reservoir 74 bycapscrews 76. The reservoir 74 has a fitting 77 at its lower end and amanifold 78 is threaded into the fitting. The manifold 78 is in fluidcommunication with corresponding manifolds 79 (FIG. 1) provided on theleveling sensors 70, 72, and 73, respectively. Such fluid communicationis provided by a common conduit 80.

The neck portion 75 is provided with an axial bore 81 and a threadedplug 82 having an axial bore 83 is provided at one end of the bore 81.The other end of the bore 81 is closed by a cap 84 and by a plug 85. Thecap 84 has a cylindrical projec- I tion 86 which is pivotally attachedto the beam 12 by a clevis 87 so that the leveling sensor 71 may bemaintained in a vertical position by its weight for all platenpositions.

A float 88 is provided in the reservoir 74. The float 88 has a weight 89attached thereto so that the float is maintained in a vertical position.The upper end of the float 88 is provided with an axially projecting rod90 having a soft iron rod 91 attached to its upper end. The soft ironrod 91 comprises the core of a linear variable differential transformer(LVDT), which includes the core 91 movable within the bore 81. Withinthe bore 81 and surrounding the core 91 there are provided windings 92which include two identical secondary windings and a primary winding. Asis conventional in linear variable differential transformers, when thecore 91 is in a predetermined null position, the voltage output from thesecondary windings are the same. When the core 91 is moved from itspredetermined null position, however, the voltage output of one of thesecondary windings increases and the voltage output of the othersecondary windings decreases. depending upon the direction and extent ofcore movement.

Signals generated by the linear variable differential transformerassociated with the leveling sensor 71 are transmitted to theservocontrollers 44 associated with the rams 25 and 26.

Similarly, signals generated by the linear variable differentialtransformer associated with he leveling means are transmitted to theservocontrollers 44 associated with the rams 27 and 28. Signalsgenerated by the linear variable differential transformer associatedwith the leveling means 72 are transmitted to the servocontrollers 44associated with the rams 3] and 32 and signals generated by the linearvariable differential transformer associated with the leveling means 73are transmitted to the servocontrollers 44 associated with the rams 33and 34.

Each reservoir 74 is partially filled with a liquid 93 and the liquid ineach reservoir 74 is in communication with the liquid in all otherreservoirs through the manifolds 78 and 79 and the conduit provided onthe leveling means 70, 71, 72, and 73. When the fluid-connected levelingsensors are level with respect to each other, a float in one levelingsensor is at the same level as the float in the other leveling sensors.Thus, when the leveling sensors 70, 71, 72, and 73 are at the sameelevation, the floats 88 in all of the leveling sensors are at the samelevel and the cores 91 all establish zero outputs for their associatedlinear variable differential transformers. lf, however, a heavier loadexists in the area supported by the rams 27 and 28, for example, and theremaining rams and the leveling sensors 71, 72, and 73 are slightlyhigher than the rams 27 and 28 and their leveling sensor 70 (even thoughequal pressures exist in all of the rams), the cores 9] in the levelingsensors 71, 72, and 73 will be retracted somewhat from their nullposition and the core associated with the leveling sensor 70 will beadvanced somewhat from its null position. A signal will be transmittedby the linear variable differential transformer associated with theleveling sensors 71, 72, and 73 to the servocontrollers 44 associatedwith the rams 25, 26, 31, 32, 33, and 34 to modulate the output signalof the servocontrollers 44 to direct the valves 42 to exhaust fluid fromthe rams 25, 26, 31, 32, 33, and 34. Similarly, the signal generated bythe linear variable differential transformer associated with theleveling sensor 70 will generate a signal directing the servocontrollersassociated with the rams 27 and 28 to direct the valves 42 to add fluidto the rams 27 and 28 until the linear variable differentialtransformers again achieve a null position. It should be noted that thesignals generated by the linear variable differential transformersoverride and correct the signal transmitted by the pressure transducer55.

There is provided on each leveling sensor 70 to 73 a sight glass so thatvisual observation may be made of the fluid in any sensor. Each sensor70 to 73 is also provided with an overflow outlet and air vent 101(FIG. 1) so that in the event that a sensor does not pivot properly,fluid will be dumped through the vent 101 rather than flowing into theprimary and secondary coils of the linear variable differentialtransformers.

It should be appreciated that other linear or angular motion sensors maybe employed in conjunction with this invention.

For example, the linear motion sensors associated with the levelingsensors may be linear motion variable inductors or linear motionvariable capacitors. Furthermore angular motion may be sensed by angularmotion variable capacitors, rotary variable differential transformers,variable reluctance angular position transducers, or the like.

What is claimed is:

l. A platen raising, lowering, and leveling system comprising a platen,ram means for positioning said platen at a preselected position, saidram means including master ram means and slave ram means, valve meansassociated with each ram means to admit and exhaust fluid pressure toand from each ram means, control means for each valve means, means togenerate one of a multiplicity of command signals to the control meansassociated with he valve means controlling said master ram means, saidcontrol means, in response to a command signal, operating said masterrarn valve means until said master ram means attains a desired positioncorresponding to the value of said command signal, position sensingmeans associated with said platen to determine the actual position ofsaid platen, means responsive to said position-sensing means to generatean error-correcting signal to the control means associated with thevalve means controlling said master rams means said associated controlmeans operating its valve to correct any error in the position of themaster ram signalgenerating means responsive to the pressure in saidmaster ramand adapted to transmit a signal to each other control meansas a function of the fluid pressure in the master ram means, each ofsaid other control means operating its valve means in response to saidsignal so that each slave ram means attains a pressure corresponding tothe pressure of said master ram means, means to compare any differencein the actual extended level of at least one slave ram on the one handwith the actual extended level of at least one other slave ram on theother hand, means for generating an error-correcting signal as afunction of any level differences between said slave rams, and means forfeeding the error-correcting signal to said other control means tomodulate and correct the signal transmitted to said other control meansfrom the pressure-responsive signal-generating means. I

2. A platen raising, lowering, and leveling system comprising anassembly platen and a support platen, said platens being hinged togetheralong one edge, ram means for each platen having piston rods pivotedadjacent the opposite edge of each platen and adapted to pivot eachplaten between substantially horizontal and substantially verticalpositions, said ram means including master ram means and slave rammeans, valve means associated with each ram means to admit and exhaustfluid pressure to and from each ram means, control means for each valvemeans, means to generate one of a multiplicity of command signals to thecontrol means associated with the valve controlling said master rammeans, said control means in response to a command signal operating saidmaster ram valve means until said master ram means attains a desiredposition corresponding to the value of said command signal,positionsensing means associated with each of said platens to determinethe actual positions of said platens, means responsive to saidposition-sensing means to generate an error-correcting signal to thecontrol means associated with the valve controlling said master rarnmeans, said associated control means operating its valve to correct anyerror in the position of the master ram means, signal-generating meansresponsive to the pressures in said master ram means and adapted totransmit a signal to each other control means as a function of the fluidpressure in the master ram means, each of said other control meansoperating its valve means in response to said signal so that each slaveram means attains a pressure corresponding to the pressure of saidmaster ram means, means to compare any differences in the actualextended level of at least one slave ram on the one hand with the actualextended level of at least one other slave ram on the other hand, meansfor generating an error-correcting signal as a function of any leveldifferences between said slave ram means, and means for feeding theerror-correcting signal to said other control means to modulate andcorrect the signal transmitted to said other control means from thepressure-responsive signal-generating means.

3. A platen raising, lowering, and leveling system according to claim 1,wherein said means to compare any differences in the actual extendedlevel of at least one slave ram on the one hand with the actual extendedlevel of at least one other slave ram on the other hand comprises aplurality of reservoir means connected together by fluid conduit means,each of said reservoir means having float means contained therein, eachof said fluid reservoir means being pivotally connected to the platenadjacent one of the slave ram means, and wherein said means forgenerating an error-correcting signal as a function of any leveldifferences between said slave ram means comprises rod means connectedto each of said float means, coil means surrounding each rod means togenerate said errorcorrecting signal as a function of any differences inlevel of said float means.

4. A platen raising, lowering, and leveling system according to claim 1,wherein said position-sensing means associated with said platen todetermine the actual osition of said platen comprises a gear segmentfixed to said p aten, spur gear means meshing with said segment gear,and wherein said means responsive to said position-sensing meansincludes an angular motion potentiometer driven by said spur gear whichgenerates said error-correcting signal to the control means associatedwith the valve controlling said master ram means.

5. A platen raising, lowering, and leveling system comprising a platen,ram means for positioning said platen at a preselected position, saidram means including master ram means and slave ram means, means to admitand exhaust fluid pressure to and from each ram means, means to sensethe fluid pressure in said master ram means and to provide that pressurein each of said slave ram means, means to compare any differences in theactual extended level of at least one slave ram on the one hand with theactual extended level of at least one other slave ram on the other hand,and means to correct any level differences between said slave rams.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.

34638535 Dated February 1. 1971 Inventor(s) Robert J Ponter v It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 20, change "mail" to --main-.

Column 1, line 23, change "of" to --or--.

Column 4, line 43, after "the" insert signals generated by the pre ssuretransdncers 51 to 54 and 56 to 60 and the.

Column 4, line. 69, change "he" to --the--.

Signed and sealed this 13th day of June 1972 (SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR.FAttesting Officer

1. A platen raising, lowering, and leveling system comprising a platen,ram means for positioning said platen at a preselected position, saidram means including master ram means and slave ram means, valve meansassociated with each ram means to admit and exhaust fluid pressure toand from each ram means, control means for each valve means, means togenerate one of a multiplicity of command signals to the control meansassociated with he valve means controlling said master ram means, saidcontrol means, in response to a command signal, operating said masterram valve means until said master ram means attains a desired positioncorresponding to the value of said command signal, position sensingmeans associated with said platen to determine the actual position ofsaid platen, means responsive to said positionsensing means to generatean error-correcting signal to the control means associated with thevalve means controlling said master rams means said associated controlmeans operating its valve to correct any error in the position of themaster ram signal-generating means responsive to the pressure in saidmaster ram and adapted to transmit a signal to each other control meansas a function of the fluid pressure in the master ram means, each ofsaid other control means operating its valve means in response to saidsignal so that each slave ram means attains a pressure corresponding tothe pressure of said master ram means, means to compare any differencein the actual extended level of at least one slave ram on the one handwith the actual extended level of at least one other slave ram on theother hand, means for generating an error-correcting signal as afunction of any level differences between said slave rams, and means forfeeding the error-correcting signal to said other control means tomodulate and correct the signal transmitted to said other control meansfrom the pressure-responsive signal-generating means.
 2. A platenraising, lowering, and leveling system comprising an assembly platen anda support platen, said platens being hinged together along one edge, rammeans for each platen having Piston rods pivoted adjacent the oppositeedge of each platen and adapted to pivot each platen betweensubstantially horizontal and substantially vertical positions, said rammeans including master ram means and slave ram means, valve meansassociated with each ram means to admit and exhaust fluid pressure toand from each ram means, control means for each valve means, means togenerate one of a multiplicity of command signals to the control meansassociated with the valve controlling said master ram means, saidcontrol means in response to a command signal operating said master ramvalve means until said master ram means attains a desired positioncorresponding to the value of said command signal, position-sensingmeans associated with each of said platens to determine the actualpositions of said platens, means responsive to said position-sensingmeans to generate an error-correcting signal to the control meansassociated with the valve controlling said master ram means, saidassociated control means operating its valve to correct any error in theposition of the master ram means, signal-generating means responsive tothe pressures in said master ram means and adapted to transmit a signalto each other control means as a function of the fluid pressure in themaster ram means, each of said other control means operating its valvemeans in response to said signal so that each slave ram means attains apressure corresponding to the pressure of said master ram means, meansto compare any differences in the actual extended level of at least oneslave ram on the one hand with the actual extended level of at least oneother slave ram on the other hand, means for generating anerror-correcting signal as a function of any level differences betweensaid slave ram means, and means for feeding the error-correcting signalto said other control means to modulate and correct the signaltransmitted to said other control means from the pressure-responsivesignal-generating means.
 3. A platen raising, lowering, and levelingsystem according to claim 1, wherein said means to compare anydifferences in the actual extended level of at least one slave ram onthe one hand with the actual extended level of at least one other slaveram on the other hand comprises a plurality of reservoir means connectedtogether by fluid conduit means, each of said reservoir means havingfloat means contained therein, each of said fluid reservoir means beingpivotally connected to the platen adjacent one of the slave ram means,and wherein said means for generating an error-correcting signal as afunction of any level differences between said slave ram means comprisesrod means connected to each of said float means, coil means surroundingeach rod means to generate said error-correcting signal as a function ofany differences in level of said float means.
 4. A platen raising,lowering, and leveling system according to claim 1, wherein saidposition-sensing means associated with said platen to determine theactual position of said platen comprises a gear segment fixed to saidplaten, spur gear means meshing with said segment gear, and wherein saidmeans responsive to said position-sensing means includes an angularmotion potentiometer driven by said spur gear which generates saiderror-correcting signal to the control means associated with the valvecontrolling said master ram means.
 5. A platen raising, lowering, andleveling system comprising a platen, ram means for positioning saidplaten at a preselected position, said ram means including master rammeans and slave ram means, means to admit and exhaust fluid pressure toand from each ram means, means to sense the fluid pressure in saidmaster ram means and to provide that pressure in each of said slave rammeans, means to compare any differences in the actual extended level ofat least one slave ram on the one hand with the actual extended level ofat least one other slave ram on the other hand, and means to correct anylevel differences between said sLave rams.